Conventional fairy lights that decorate Christmas trees are composed of many light bulbs, and require being uniformly disposed on the Christmas trees so as to exhibit the appearance of the Christmas trees at night. However, with the development of package technology, LEDs that have the advantages of small size, high shock resistance, low power consumption, long lifetime, no warm up time and fast response time have gradually replaced the conventional light bulbs.
Referring to FIG. 1, FIG. 1 is a cross-sectional schematic diagram illustrating a light-emitting device package structure applied to Christmas trees according to the prior art. As shown in FIG. 1, the light-emitting device package structure 10 includes a leadframe 12, a light-emitting device 14 and an encapsulant 16. The leadframe 12 has two leads 18. The light-emitting device 14 is mounted on the leadframe 12, and an anode and a cathode of the light-emitting device 14 are electrically connected to the leads 18 by two respective wires 20. The encapsulant 16 is a hemispherical lens structure encapsulating the light-emitting device 14, and a center of a cambered surface of the hemispherical lens structure disposed on the light-emitting device 14 has a concavity with an upside down conoid shape. The light (indicated by the arrow shown in FIG. 1) emitted from the light-emitting device 14 can be reflected by the concavity 22 while passing though the concavity 22, and then emitted to an edge of the light-emitting device package structure 10. Therefore, a luminous angle is increased.
Referring to FIG. 2, FIG. 2 is a schematic diagram illustrating a relation between luminous intensity and luminous angle of the light-emitting device package structure according to the prior art. As shown in FIG. 2, the luminous intensity of the light-emitting device package structure can be detected at the luminous angle between positive 90 degrees and negative 90 degrees. This means that the light-emitting device package structure from the optical axis to 90 degrees deviated to the edge emits light, so that the light-emitting device package structure has a certain luminous intensity at the luminous angle from positive 90 degrees to negative 90 degrees. Therefore, when the light-emitting device package structure is disposed on the Christmas tree, the Christmas lamp can be clearly viewed from all kinds of angles below the Christmas tree.
Although the light-emitting device package structure according to the prior art can emit light at the luminous angle of 90 degrees, the luminous intensity at the optical axis of the light-emitting device package structure is reduced by the concavity. The reduced luminous intensity is substantially at the luminous angle between positive 20 degrees and negative 20 degrees. Therefore, when the light-emitting device package structure according to the prior art is applied to the Christmas tree, the viewing distance between the viewer and the Christmas tree is limited because of the limit of the luminous intensity of the light-emitting device package structure. To increase the luminous intensity at the optical axis of the light-emitting device package structure and to keep the luminous intensity at the edge of the light-emitting device package structure are important objectives to be achieved.